The present invention relates to cleaning method and apparatus for cleaning a film deposition apparatus that performs a film deposition process upon a semiconductor wafer or the like.
Generally, in the manufacturing process of a semiconductor integrated circuit, various kinds of processes, for example, film deposition process, oxidation/diffusion process, etching process, surface modification process, etc. are repeatedly performed upon a surface of a semiconductor wafer as an object to be processed. Then, as occasion demands, a cleaning process for removal of an unnecessary film adhering to the interior of a processing container forming a processing apparatus is performed to prevent an occurrence of particles that might cause a yield rate for production to be reduced. Especially in the film deposition process, since there are produced metal films of various elements, for example, W, WSi, Ti, TiN, etc. in addition to a proper polysilicon film, an etching process effective to these metal films is desired eagerly.
In the above-mentioned cleaning method, there exist a known plasma cleaning method where a cleaning gas is activated by using a plasma and another thermal cleaning method where a plasma is not employed but a cleaning gas is introduced into a heated processing container. In the plasma cleaning method, it is general that NF type gas (e.g. NF3 gas) or HF type gas (e.g. HF gas) is employed as the cleaning gas because it is relatively difficult for only heat to resolve these gases. While, in the thermal cleaning method, CIF type gas, such as CIF3, is mainly used for the cleaning gas because the same gas exhibits a high resolvability and can be resolved by only heat with ease. In the plasma cleaning method, there are drawbacks that the method requires a plasma generating mechanism and cannot clean anything besides an area where a plasma is generated. To the contrary, because of the absence of such drawbacks, the thermal cleaning method is apt to be employed frequently.
Taking it for granted that all of unnecessary supplementary films should be eliminated by a cleaning process, one of the most important things in common with both of the above mentioned cleaning methods is to carry out an etching process with a necessary and sufficient period while considering that the etching process does not injure various kinds of structures in the processing container. Namely, it means that an excessive etching should be avoided with determination of an optimum end point in the etching process. On the contrary, if performing the etching process excessively, then result in the waste of expensive cleaning gas and reduce operating time of the apparatus.
Referring to the detection for the xe2x80x9cetchingxe2x80x9d end point in the conventional cleaning method, if the processing container is provided with an observation window, then an operator used to confirm the cleaning condition by visually confirming the interior of the processing container through the observation window thereby to determined the etching end point. Besides, as shown in Japanese Patent Publications Nos. 9-82645 and 9-143742, pressure detecting means is provided for monitoring a pressure inside the processing cointainer, so that the etching end point is determined on basis of a change in pressure.
When monitoring a pressure in the above way, however, a problem arises in that the apparatus has to be provided with the pressure detecting means additionally. While, in case of visual confirmation through the observation window, a problem arises in the existence of differences among individuals in detecting the etching end point. To begin with, if no observation window is provided for the apparatus, it is impossible to apply the above detecting method by means of the observation window.
Besides, in conformity with one""s experience, it has been attempted to establish a cleaning period in accordance with an integrated time throughout the film deposition process. Nevertheless, it should be noted that the film-deposition rate differs from one processing condition to another. Furthermore, a quantity of deposited film differs from one component in the processing container to another. For these reasons, it is difficult to determine an appropriate cleaning period uniformly.
Paying attention to the above-mentioned problems, the present invention is provided to solve these problems effectively. The object of the present invention is to provide cleaning method and apparatus for a film deposition apparatus, both of which allow a proper end point of etching to be detected with ease.
As a result of studying the cleaning process diligently, the present invention is produced on the ground of our knowledge that if an unnecessary film to be cleaned is eliminated by the cleaning operation under a constant process, then an amount of gas resulting from the resolving reaction is decreased, so that the opening degree of an automatic pressure regulating valve is reduced as much.
The present invention resides in a cleaning method of eliminating an unnecessary film adhering to the interior of a processing container of a film deposition apparatus by using a cleaning gas, the processing container being capable of forming a vacuum by a vacuum exhausting system, the method comprising the steps of: introducing the cleaning gas of a predetermined quantity into the processing container and also controlling an opening degree of an automatic pressure regulating valve provided in the vacuum exhausting system thereby to maintain the interior of the processing container at a predetermined pressure and monitoring the opening degree of the automatic pressure regulating valve; and also detecting a situation that the opening degree has changed from an opening degree of the automatic pressure regulating valve in its stable condition in excess of a predetermined amount thereby to recognize an end point of an etching on a basis of detection of the situation.
In this way, by performing the cleaning operation so that the automatic pressure regulating valve usually attains a constant pressure in the processing container, when an unnecessary film to be eliminated in the cleaning operation vanishes, a gas produced by the resolving reaction decreases, so that the pressure in the processing container is apt to drop as much. Consequently, this change of the pressure in the processing container causes an opening degree of the automatic pressure regulating valve to be decreased in order to cancel the above change, so that the pressure in the processing container is maintained to a generally-constant value finally. Therefore, by monitoring the opening degree of the automatic pressure regulating valve, it becomes possible to recognize the appropriate end point of etching when it is detected that the opening degree has decreased more than the predetermined amount.
In this case, the end point of the etching may be identical to a point of time when it is detected that the opening degree has changed more than the predetermined amount. Alternatively, as prescribed, the end point of the etching may be identical to a point of time when a predetermined period has passed since a point of time when it was detected that the opening degree had changed more than the predetermined amount.
As prescribed for example, the predetermined period is within a range from 10 to 30% of a period from a start point of the etching till the point of time when it is detected that the opening degree has changed more than the predetermined amount.
Further, as prescribed for example, the monitoring step of the opening degree is accomplished by motoring a control voltage for driving the automatic pressure regulating valve.
Further, as prescribed for example, the cleaning gas is identical to a ClF-gas and the etching is identical to a thermal cleaning using no plasma.
The present invention as claimed resides in an apparatus for carrying out the method prescribed, the apparatus comprising a processing container in which a mounting table for mounting an object to be processed thereon is accommodated, a cleaning-gas supplying means for supplying a cleaning gas into the processing container, a vacuum exhausting system for exhausting an atmosphere in the processing container in vacuum, an automatic pressure regulating valve interposed in the vacuum exhausting system so that a pressure in the processing container can be maintained at a constant pressure by changing an opening degree of the automatic pressure regulating valve, a valve-opening monitoring means for monitoring the opening degree of the automatic pressure regulating valve, a change detecting means for detecting a change in the opening degree on a basis of an output from the valve-opening monitoring means and a cleaning-end-point recognizing means for recognizing an end point of a cleaning operation on a basis of an output from the change detecting means.